1. Field of the Invention
The invention relates to a belt type continuously variable transmission which can achieve a desired speed ratio by changing a winding radius of a belt.
2. Description of the Related Art
A belt type continuously variable transmission has been known as a transmission for a vehicle. The belt type continuously variable transmission of this type includes a primary shaft (a rotating shaft on the driving side) and a secondary shaft (a rotating shaft on the driven side) which are provided in parallel with each other; a primary pulley which is attached to the primary shaft; and a secondary pulley which is attached to the secondary shaft. Each of the primary pulley and the secondary pulley includes a fixed sheave, and a movable sheave which is movable with respect to the fixed sheave. Each movable sheave is provided so as to be movable in the axial direction and immovable in the circumferential direction with respect to the corresponding rotating shaft via a ball, a ball groove (ball spline), and the like. A substantially V-shaped pulley groove is formed between the fixed sheave and the movable sheave. An endless belt is wound on the pulley grooves of the primary pulley and the secondary pulley. A pulley hydraulic chamber for making the movable sheave come close to/move away from the corresponding fixed sheave is provided for each of the primary pulley and the secondary pulley. The hydraulic pressure of the pulley hydraulic chamber for the primary pulley and the hydraulic pressure of the pulley hydraulic chamber for the secondary pulley are controlled separately. Thus, a groove width of the pulley is changed, and therefore a belt winding radius is changed. As a result, a speed ratio of the belt type continuously variable transmission is set to a desired value, and a tension of the belt is adjusted.
Japanese Patent Application Publication JP(A) 11-141633 discloses a technology related to the above-mentioned belt type continuously variable transmission. In this belt type continuously variable transmission, oil passages for supplying hydraulic fluid to the above-mentioned pulley hydraulic chamber are formed along the axis of a pulley shaft and in the radial direction of the pulley shaft, and the radial direction oil hole is formed in a spline shaft portion of the pulley shaft on the shaft end side. The movable sheave is attached to the spline shaft portion by spline-coupling. As a result, concentration of stress that occurs in the oil hole is reduced.
According to the technology disclosed in Japanese Patent Application Publication JP(A) 11-141633, the radial direction oil hole is formed in the spline shaft portion on the shaft end side, and therefore concentration of stress that occurs in the oil hole can be reduced to a certain extent. However, since the radial direction oil hole is formed in an area between two bearings which support the pulley shaft, the pulley shaft may be deformed by a bending load due to a belt tension applied to the pulley shaft, and the stress may be concentrated on the radial direction oil hole. As a result, considering the concentration of stress, the number of the radial direction oil holes need to be reduced, a diameter of the oil hole need to be decreased, or a diameter of the pulley shaft need to be increased, which causes problems such as an increase in cost and an increase in weight.